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INDUSTRIAL AND EKGINEERING CHEMISTRY
(18) Prandtl, L., Phusik. Z . , 11, 1072-8 (1910). (19) Reynolds, O., Scientific Papers, Vol. 1, pp. 81-5, Cambridge Univ., 1900. (20) Rouse, H., “Fluid Mechanics for Hydraulic Engineers”, New York, McGraw-Hill Book Co., 1938. (21) Sherwood, T. K., Kiley, D. D., and Mangsen, G. E., Trans. Am. Inst. Chem. Engrs.,28, 154-70 (1932); IXD. EXG.CREM., 24, 273-7 (1932). (22) Taylor, G. B., Chilton, T . H . , and Handforth, S. L., Ibid., 23, 860-5 (1931).
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(23) Taylor, G. I., Brit. Advisory Comm. Aeronautics, Rept. and ilfemo. 272 (1917). (24) Thiesenhusen, H . , Gesundh. Ing., 53, 113-19 (1930). (25) Walker, W. H., Lewis, IT.K., Mcridams, W.H., and Gilliland, E. R., “Principles of Chemical Engineering”, 3rd ed., New York, McGraw-Hill Book Co., 1938. (26) White, A. H., Trans. Chem. Eng. Congr. nrorld Power Con!., London, 193G, 4, 93-117; “Twenty-five Years of Chemical Engineering Progress”, pp. 351-62, Am. Inst. Chem. Engrs.. 1933.
CASEIN PLASTICS GEORGE H. BROTHER, U. S. Regional Soybean Industrial Products Laboratory, Urbana, 111.1
EW industries offer greater possibilities to the research chemist than the plastics industry. The polymerization and condensation reactions which form the plastic resins are not only complicated and little understood, but in many cases the starting materials are of unknown structure. Therefore, since so little is known about plastic materials, i t is surprising how widely they have been successfully applied in spite of this handicap. With’more fundamental knowledge of their structures and properties available, more intelligent applications would be possible in present fields and probably in fields not as yet considered. This is especially true of casein plastics. Casein is a protein, a class of material that has baffled chemists since the time of Emil Fischer. However, there has been a change in the attitude of research chemists recently with the application of the x-ray, the infrared ray, the ultracentrifuge, the monomolecular film, etc., to the study of the structure of proteins. Preliminary results on the investigation of protein have already been obtained with these tools, which hold promise for the future of the whole class in general and for casein plastic material in particular.
F
Manufacture Casein plastic is the result of a reaction between casein and formaldehyde. The commercial possibilities of the hornlike product of this reaction were first appreciated about 1897 by Adolf Spitteler (2f,25), a German chemist. Through the early years of development considerable trouble was encountered chiefly because of the extremely clumsy process of production. This process consisted essentially of dispersing the casein in a n aqueous solution of some alkali, coagulating the dispersion with a n acid or an acid salt, pressing the wet curd into plates, and soaking these plates in formaldehyde solution until they harden. Throughout this period the industry was entirely controlled by the GermanFrench firm, Internationale Galalith-Gesellschaft Hoff & Compagnie, located a t Harburg, Germany, and the product was called “Galalith”, meaning milkstone. This firm is still in business and is probably the largest casein plastics manufacturer in the world. Its product is so well known by the trade t h a t Galalith has practically become a generic term applied to all casein plastic material. 1 A cooperative organization participated in by the Bureaus of Agricultural Chemistry and Engineering and of Plant Industry of the United States Department of Agriculture. and the Agricultural Experiment Stations of the North Central States of Illinoia, Indiana, Iowa, Kansas, hfichigan, Minnesots, hlissouri. Nebraska, North Dakota, Ohio, South Dakota, and Wiaaonein.
During or shortly after the World K a r , it was found that rennet casein could be satisfactorily plasticized by heat and pressure if the total moisture content was about 40 per cent. The powdered casein used was dry, as far as appearance and methods of handling were concerned, and the process was consequently known as the dry process. The Erinoid Company of England ( 1 , IO), so named because of large Irish interests, after experimenting unsuccessfully with the wet process for a number of years finally succeeded with the dry process in making a product which is still the leading British casein plastic material today. The first American casein plastic material was Aladdinite, followed by Karolith, Kyloid, Inda, and finally by American Erinoid. These were all satisfactory, as far as the products were concerned, but were not established on a profitable economic basis in this country. There are two principal reasons for this failure: ( a ) The climatic conditions in America are different from those in Europe, and as a result, casein plastic material must be restricted to buttons, buckles, and other small objects. ( b ) The process of manufacture is long and expensive, the material itself is not adapted to fabrication on automatic machines, and there is no profitable outlet for the large proportion of waste. Accordingly, Karolith, the Erinoid Company of America, and Pan-Plastics merged in 1931 to form the American Plastics Corporation. Their product, Ameroid, is the only casein plastic material of domestic origin available today. The dry process for the manufacture of casein plastic material, as previously indicated, is based upon the plasticization of casein powder, containing about 40 per cent total moisture, by the simultaneous action of heat and pressure (20). These are usually applied in screw cylinder presses, such as are used in the rubber industry for the extrusion of rods. The soft plastic is extruded as rods or tubes, depending on the mandrel used. If sheets are required, the rods are flattened out in hydraulic presses to fill frames of the required size. Button blanks may be sliced from the rods or punched from the sheets. Dyestuff or fillers, as desired, are introduced with the water before plasticization. Mottled or streaked effects are produced by mixing small pieces or “buttons” of previously formed soft plastic (16) of the desired color into the powder before extrusion. The rods and sheets of soft plastic must be hardened by immersion in a bath of aqueous formaldehyde solution of about 4 per cent concentration for a period of about 3 weeks to 6 months, depending upon the thickness of the material. After hardening, the material must be dried to the normal moisture content of 8 to 12 per cent. The drying process requires about the same length of time as the hardening. Obviously such a course of manufac-
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VOL. 32, NO. 1
manufacture of Aladdinite. The buttons turned to shape, either by automatic machines from blanks sliced from the cold soft plakic (17) or directly from alum casein rods, harden in formaldehyde in a few days. Although these and other coneerns follow the plan of uniting the button factory directly to a casein plastics plant, the smaller operators buy hardened button blanks of Ameroid. These cannot be used as efficiently as the soft plastic hiit are much better than sheets or rods, from which the waste is sometimes as high as 50 per cent. Some mention has heen made of hnttons molded t o shape from soft plastic in sheets connected by thin fins (2). Buttons which have been molded can he punched out and hardened in formaldehyde in the same manner as those turned. In either case there is no waste, as the turnings or fins of soft or alum casein call be reworked, and the time of hardening is a matter of a few days. After hardening, the buttons are drilled in automatic machines and polished by treatment with a hot sodium or calcium liypochlorite solotion. This so-called chemical or dip polish (8,24) really produces a surface glaze which, it is claimed, also renders the material more water resistant. The buttons are usually given a final short tumbling with wax and wooden pegs, and they are then ready for grading and shipping.
Technical I m p r o v e m e n t s
ture ties up an inordinate amount of material in process, and hence in capital, and is expensive without counting the amount or material lost as a result of spontaneous fractures.
HuLtons from Plastics The American button manufacturers have found a way t o overcome most of these difficulties, and they must be given credit for building up a business which produces about 4000 tons of casein plastic buttons and buckles annually. They have accomplished this by the simple, nontechnical, coinmonSense move of combining the button factory and the casein plastics plant, with the result that waste is largely eliminated, and the partially fabricated button is thin enough to harden and season so rapidly that the cycle of production has been reduced to about a week. The annual domestic production of casein plnstics finished as sheets and rods has dropped to about 50 tons, with a negligible amount imported. George Morrell, a button manufacturer, bought the struggling Kyloid plant in 1928 and joined it directly t o his button factory. The following year, Christensen, who had developed Aladdinite, found that alum (8) mixed directly with the water before ext.rusion, partially hardened the casein so that rods extruded from this mixture could be turned in automatic screw machines much more satisfactorily than either the soft plastic or the formaldetiyde-har~ened casein plastic. He formed the Button Corporation of America about 1931 t o produre buttons by this process and discontinued the
Technically, the attempts t o improve the process of manufacture of casein plastic material have followed two lines-namely, shortening the tinlo of hardening by the incorporation of a salt such as ainmonium chloride (22) or thiocyanate (22) in the powder before extrusion, and substitution of a dormant hardening agent for the formaldehyde bath. These latter agents have iisually taken the form of trioxymethylene (25), hexainethylcnetetrainine (S), or repressing agents such as formamide ( 8 ) , dicyandiamide (I@, hydroaromatic alcohols or kctones (22) with formaldehyde. The object of all OF these attempts was t o permit the plast,ic to flow to shape and then have the hardening agent become active and harden the protein material. So far as can he determined, noiie of these experiments was sufficiently successful to warrant a coniniercial development. Receiitly it has been found possible to produce a thernioplastic formaldehyde-hardenLul protein material (5) that may be formed to shape under the influence of heat and pressure and come finished from the die. The protein powder is treated with 40 per cent formaldehyde solution so adjusted with alkali that the pII of the equilibrium solution over the protein will be that of the isoelectric point of the protein. The excess formaldehyde is washed out with water and the formaldehyde-protein powder dried to normal moisture content or less. The moisture content may be reduced to 5 per cent or less, and a plasticizer, such as ethylene glycol ( 6 ) , ethylene cyanohydrin, glycerol, etc., added. Acid casein rather t h a n rennet casein was found to give the best products by this treatment, the degree of hydrolysis appearing to affect the water absorption inversely (4). I n every case, even when u p t o 20 p r cent ethylene glycol was used as a plasticizer, the water ahsorption of this thermoplastic formaldehydehardened protein materid was found t o k less than the water absorption of casein plastic material p r e pared hy the usual dry process which was 18 to 25 per cent. Acid casein hardened with formaldehyde and molded with 15 per cent moisture present gave a water absorption of approximately 10 per cent, while that with a moisture content of about 5 per cent and ethylene glycol content of 15 per
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
cent gave about 15 per cent water absorption. The length of all tests was 24 hours. This development is not of as great commercial importance as it would have been ten years or so ago. As the plastics industry is operated today, the only thermoplastic material of any interest or importance must lend itself to application of injection molding. I n this process the plastic is heated considerably above its yield point and then forced into comparatively cool dies where i t sets almost immediately and can be discharged. A cycle of tn.0 discharges per minute is not a t all unusual for injection molding machines. Thermoplastic formaldehyde-hardened casein material is not sufficiently fluid to work in a n injection machine, and to date a plasticizer has not been foiind that will render i t applicable. Here is a field of worth while research and one that promises a n ample reward for successful efforts. The material principally used in injection dies a t the present time is cellulose acetate plastic, selling a t about 80 cents per pound. Casein plastics could compete very favorably as far as color range is concerned. I n case a plasticizer could be discorered that would also improve the water resistance, casein plastics might well be brought to a practical comparative basis for most applications, and applications not as yet, considered would be possible because of the cheaper material.
Thermosetting Compounds The other type of plastic material of commercial importance is the thermosetting, such as molding compounds with phenolic or urea resin bases. Pieces molded from thermosetting powders may be removed from the hot die without chilling. Many attempts have been made to combine casein with phenolic (13, 2s) or urea (18) resinous molding compounds, largely in the capacity of filler material. There is, however, only one well-known instance of such a combination having a successful commercial application-namely, that of an automobile manufacturer who uses soybean meal (14) in a phenolic molding mixture primarily for gearshift knobs and horn buttons. Recent experiments, the results of which have not yet been published, indicate, however, that the thermoplastic formaldehyde-hardened protein may be modified advantageously with either phenolic or urea resins to produce thermosetting molding powders of considerable potential commercial interest. Mixtures of 50 per cent formaldehydehardened protein ( 7 ) with a moisture content of 3 per cent or less, compounded with 25 per cent phenolic resin and 25 per cent wood flour may be pressed a t 330" F. and 2000 pounds per square inch into unit pieces having good strength and closely resembling the regular phenolic material in appearance, except that they are more translucent. A good range of colors is possible, but they have not as yet been tested for light fastness. The water absorption which is about 3 per cent in 48 hours of immersion is higher than that of the regular phenolic plastics but much less than that of any protein plastic material. This hardened protein material mixed with an equal portion of urea resin in place of alpha-cellulose, commonly used as filler, produces a good molding powder which is also thermosetting. The molded pieces are translucent, may be produced in any color or shade except pure white, and have a water absorption of about 5 per cent. The pieces do not soften or swell in water, nor do they fracture on drying. A difficult chemical problem will have to be solved, however. before this application can have any commercial importance. The problem arises from t!he fact that the formaldehydehardened protein gives a definite acid reaction when suspended in nater. Methylol ureas in water dispersion are set u p by acid, so that when they are mixed with proteinformaldehyde, the urea resin sets up. I t has not been possible
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up to this time to neutralize the acid reaction of the hardened protein without the addition of so much alkali that the nature of the hardened protein has been adversely affected. A fundamental study of the protein-formaldehyde complex may be necessary before this problem can be solved. This is only one of the problems whose solution awaits the fundamental investigation of casein itself and of casein complexes such as casein-formaldehyde. The industry has been seriously handicapped by the lack of fundamental information without which it is practically impossible to make intelligent application. Induqtry itself can do little to remedy this condition since industrial research must show a tangible return on money invested and, although furidammtal research almost inrariably pays a big dividend in t he long run, there are few industrial concerns willing to support adequately the long-term and uncertain program that, will be necessary to make even a good start in solving these problems. HoTTever, the time appears to be ripe to undertake this work seriously. ,4s mentioned before, the. new tools available, such as the x-ray, infrared ray, ultracentrifuge, and monomolecular film technique, have stimulated interest in the investigation of protein structure probably to the greatest extent in history. If the industrial chemists will bring their problems to research workers in the universities, government laboratories, and independent agencies, if they will watch carefully the results of the investigations underway a t these laboratories, and if they will apply the knowledge gained to their own practical problems, some of these problems will soon be solved. To summarize, the casein plastic industry has been seriously handicapped by the lack of fundamental information in the past. This is no longer necessary. Interest in the fundamental structure and properties of proteins has been aroused and much work has been and will be done along this line. The fundamental research worker and the practical industrial chemist or chemical engineer have their work cut out. If they will coordinate their work and ideas, casein plastic material may yet earn a place among the major plastic materials.
Literature Cited Anonymous, I n d . Chemist, 9, 193 (1933). Apple, L. d.,U. 9. Patent 1,766,819 (June 24, 1930). Bartels, A , French Patent 420,543 (April 6, 1911), 2nd addition. Brother, G. H., and RlcKinney, L. L., Brit. Plastics, 10, No. 113, 248-51 (1938). Brother, G. H., and McKinney, L. L., ISD. ENG.CHEY., 30, 1236-40 (1938). Ibid ,31,84-7 (1939). Brother, G. H., and McKinney, L. L., M o d e r n Plastics, 16, No. 1, 41, 70 (1938). Christensen, P. C., U. S. Patent 2,097,144 (Oct. 26, 1937). Dangelmajer, C., Ibid., 2,101,574 (Dec. 7, 1937). Dodd, Robert, T r a n s . I n s t . P2astics I n d . (London), 5, No. 10, 58 ( 1936). Dumont, H., German Patent 593,224 (Feb. 23,1934). Durnont, H., U. S. Patent 1,992,478 (Feb. 26, 1935). Goldsmith, B. B., I h i d , 840,931 (Jan. 8, 1907). Lougee, E. F., Modern Plastics, 13, 13, 5 4 (1936). Morin, French Patent 588,441 ( M a y 30, 1907). Morrell, George, U. S.Patent 2,103,546 (Dec. 28, 1937). Parsons, John, Ihid , 2,105,669 (Jan. 18, 1938). Redman, L. V., I h i d , 1,732,533 (Oct. 22, 1929). Ripper, K., Ibid., 1,952,941 (March 27, 1934). Simmons, TT'. H., I n d . Chemist, 6 , 206, 229, 297 (1930). Stich, Eugen, K u n s t s t o f e , 5, 158 (1915). Stock, P., German Patent 489,438 (March 4, 1926). Sturken, O., U. S. Patent 2,053,850 (Sept. 8, 1936). Vawter, TV. E , Ihid., 2,103,993 (Deo 28, 1937). Wernicke, Karl, Kunststoffe, 2, 181 (1912). PRESENTED before the Division of Agricultural and Food Chemistry at t h e 97th Meeting of the American Chemical Society, Baltimore, Md.
